                       (make-context (into (objects possible-ctx) new-objs)
                                     (attributes possible-ctx)
                                     (union (incidence possible-ctx)
-                                           (set-of [g m] | [g _ neg] counterexamples
-                                                           m (difference (attributes possible-ctx)
-                                                                         (set neg)))))
+                                           (set-of [g m] [[g _ neg] counterexamples,
+                                                          m (difference (attributes possible-ctx)
+                                                                        (set neg))])))
                       ;; certain incidence, i.e. the one given by the expert
                       (make-context (into (objects certain-ctx) new-objs)
                                     (attributes certain-ctx)

  to construct a special handler using the «make-handler»
  function. See the corresponding documentation of «make-handler»."
  [possible-ctx, certain-ctx,
   :background-knowledge #{},
   :handler default-handler-for-incomplete-counterexamples]
  (assert (set? background-knowledge))
  (assert (= (attributes certain-ctx)
             (attributes possible-ctx))

             (= counterexamples :abort)
             (recur implications nil possible-ctx certain-ctx) ; abort exploration
             ;;
             counterexamples         ; add counterexample
             (let [new-objs (map first counterexamples)]
               ;; check that new names are not there already
               (when (exists [g new-objs] (contains? (objects possible-ctx) g))
